I use a piece of wood between the frame and the floor jack,also on occasion I have put the jack under the sub frame that goes across just below the rack.not sure if thats right, thats just how I do it.
I just find a solid place to jack, then fit a jack stand under the stock jacking position, lower jack, then raise it to be just even with the stand. That way if one somehow fails (and I doubt the huge SUV jack stands are going to collapse, but you never know), there is a backup to give me time to get out from under the car.
In general, you want the cross member and the frame points right next to the wheels.
Be careful of any control arms. They have the spring attached to them, they have rubber bushings that compress a little, and they CHANGE ANGLE and the car goes up/down. It's "easy" for a jack to slip off control arms.
NEVER use a jack under a control arm as the *primary* support. It's fine as a *backup* or to help keep the car steady (from wind, or force like trying to take a bumper off), but not as a primary support.